1. Field of the Invention
The present invention relates to a large-scale radio integrated circuit (hereinafter called the “radio LSI”) which includes an interface (hereinafter called the “I/F”), conforming to IEEE (the Institute of Electric and Electronic Engineers) 802.15.4, with a physical layer (hereinafter called the “PHY”) and a data link layer including a media access control layer (hereinafter called the “MAC”) higher than the physical layer, and employs ZigBee (a trademark of ZigBee Alliance), which is one of near field radio communication standards included in radio communication standards, which divides a 2.4-GHz frequency band, the same as a radio LAN (Local Area Network) standard IEEE 802.11b, into 16 channels for utilization, and to a radio communication method, particularly, a transmission data control therefor.
2. Description of the Related Art
Conventional radio LSI's employing ZigBee and radio communication methods have been described, for example, in the following documents:
Oki Technical Review, Oki Electric Industry Co., 2004, Oct. 1, Vol. 71, No. 4, p. 24-29, 70-73 (Non-Patent Document 1); and
Japanese Patent No. 3513596 (FIG. 1) (Patent Document 1)
FIG. 1 is a communication layer model diagram showing the protocol configuration of ZigBee used in the near field radio communications described in Non-Patent Document 1 and Patent Document 1.
The protocol configuration of ZigBee employs a PHY 1 of IEEE 802.15.4 which is an international standard of WL-PAN (Wireless Personal Area Network), and a data link layer which includes a MAC 2 and a logical link control layer (hereinafter called the “LLC”), and a network layer 3 and an application I/F layer 4, higher than the layers 1, 2, are standardized in accordance with ZigBee. The application I/F layer 4 is overlaid by an application layer 5 which can be arbitrarily defined by a customer.
The PHY 1 has a data transmission/reception function such as received power measurements, link quality notification, CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance) for confirming a use situation of a channel, and the like so that received power can be measured for each channel during the construction of a network to find out a channel which is less affected by interfering power from other systems. Another mechanism has also been provided for changing to another communication channel when the quality of a used channel has deteriorated. The specifications of the PHY 1 define, for example, that the frequency is 2.4 GHz; the number of channels is 16, the modulation scheme is 0-QPSK (Quadrature Phase Shift Keying); the spreading scheme is DSSS (Direct Spread Spectrum); the data rate is 250 kbit/s; and an available area is all over the world. The data link layer has the MAC 2 which is a data format processing layer, and the LLC. The network layer 3 is a layer for managing data transfers between two nodes connected on a network.
The MAC 2 defines a beacon (BEACON) mode for performing intermittent operations and bandwidth guaranteed communications, and a non-beacon mode for making direct communications mutually among all nodes. The beacon mode is used in a star network which is centered at a network management node called the “PAN (Personal Area Network) coordinator.” The PAN coordinator periodically transmits a beacon signal, while other nodes make communications within durations assigned thereto in synchronism with the beacon signal. One node assigned by the coordinator can solely occupy a channel to make communications without collisions, and is utilized for communications for which a low latency is required. On the other hand, the non-beacon mode is a mode for accessing channels at all times in accordance with CSMA-CA. When the non-beacon mode is used in a mesh link which directly communicates with peripheral nodes, each node can directly make a communication at all times, but must be waiting for reception such that it can receive data destined thereto at all times, so that the power cannot be saved by intermittent operations as in the beacon mode.
FIG. 2 is a diagram showing a flow when ZigBee data is transmitted/received between two communication devices.
For example, when ZigBee data is transmitted/received between two communication devices 10-1, 10-2 at a radio frequency (RF) of 2.4 GHz, each communication device 10-1, 10-2 comprises a radio transmission/reception part (hereinafter called the “RF part”) 11; a modem part (MODEM) 12 for making modulation and demodulation; a PHY part 13; a PHY I/F part 14; a MAC part 15; a MAC I/F part 16; a network layer part (NETWORK) 17; an application I/F part (APPLICATION I/F) 18; an application layer part (APPLICATION) 19; and the like.
The RF part 11 is a transceiver which makes transmission/reception through an antenna at RF 2.4 GHz defined by the PHY 1 of IEEE 802.15.4. The modem part 12 modulates or demodulates data communicated with the PHY part 13 in accordance with modulation/demodulation circuit regulations defined in the PHY 1 of IEEE 802.15.4. The PHY part 13 outputs IQ data to the modem part 12 during transmission, and acquires demodulated data during reception in accordance with a data format defined in the PHY 1 of IEEE 802.15.4. The PHY I/F part 14 transmits/receives data between the PHY part 13 and MAC part 15 using a serial I/F such as a synchronous communication I/F (hereinafter called the “SCI”).
The MAC part 15 handles all MAC commands in the MAC 2 of IEEE 802.15.4. Transmission data is transferred from the MAC part 15 to the PHY part 13, modulated by the modem part 12, and transmitted from the RF part 11 and antenna. Reception data received by the antenna and RF part 11 is demodulated by the modem part 12, analyzed by the MAC part 15 through the PHY part 13 and PHY I/F part 14, and transferred to a higher rank device (network layer part 17). The MAC I/F part 16 transmits/receives data between the MAC part 15 and the network layer part 17 using a serial I/F such as SCI. The network layer part 17 transmits/receives data to/from a central processing part (hereinafter called the “CPU”) in a host using a serial I/F.
Exemplary circuit configurations for developing radio LSI's conforming to IEEE 802.15.4 and in accordance with the stipulations of ZigBee include a radio LSI 10A which is equipped with a MAC and a radio LSI 10B which is equipped with a PHY in consideration of a network configuration for each user (CUSTOMER). The MAC-equipped radio LSI 10A is a circuit that includes the RF part 11, modem part 12, PHY part 13, PHY I/F part 14, and MAC part 15, as well as the MAC I/F part 16 with a higher rank layer defined by ZigBee, and has the advantage of simplifying data transmission/reception to/from the host CPU on the higher rank layer. On the other hand, the PHY-equipped radio LSI 10B is a circuit that includes the RF part 11, modem part 12, PHY part 13, and PHY I/F part 14 conforming to IEEE 802.15.4. When the user has developed even a unique MAC, the employment of the PHY-equipped radio LSI 10B increases the degree of freedom because it can be equipped with a MAC desired by the user.
One feature of the MAC part 15 of IEEE 802.15.4 shown in FIG. 2 is the employment of a super-frame structure using a beacon. An example of this super-frame structure is shown in FIG. 3.
The super-frame structure is divided into a CAP (Contention Access Period) in which all devices can access a beacon interval; CFP (Contention Free Period) which is occupied by a particular device for accessing; and an inactive period in which all devices are prohibited from accessing. Also, the CFP is divided equally into seven by a GTS (Guaranty Time Slot) mechanism, and can be assigned to a device which wishes to preferentially make a communication. FIG. 3 shows an assignment when three time sections are assigned to GTS1 and GTS2, respectively, from seven time sections equally divided by the GTS mechanism. The devices which have been assigned this period can preferentially transmit/receive data. The beacon interval BI is set to be equal to or longer than a super-frame duration (BD).
After the beacon interval has been set using this super-frame structure, data will be transmitted/received while maintaining the same interval at all times. Therefore, IEEE 802.15.4 includes stipulations related on the beacon transmission interval (beacon interval) BI which must be observed. For this purpose, a timer is often provided within the radio LSI, and is started upon transmission of a beacon for comparing a beacon interval set value stored in an internal register with the internal timer. An interrupt is generated at a coincident time (the timer becomes equal to the beacon interval BI), such that the interrupt triggers the transmission of the beacon to maintain the interval.
FIG. 4 is a functional block diagram showing an exemplary circuit configuration of a conventional radio LSI 10B, which is equipped with the PHY, described in Non-Patent Document 1.
The PHY-equipped radio LSI 10B is a chip for serially communicating signals with a host 30 through SCI or the like, and has an RF part 11 connected to an antenna 21. The RF part 11 is connected to a modem part 12 through a serial transfer signal line, and the modem part 12 is connected to a PHY part 13 through a serial transfer signal line. The radio LSI 10B is also provided with a random access memory (hereinafter called the “RAM”) 22 for storing transmission data and the like; a bus 23 for parallelly transferring signals; a security part 24; a register, not shown; and the like. The RAM 22 is connected to the PHY part 13, security part 24, and PHY I/F part 14 through the parallel transfer bus 23, the PHY part 13 and security part 24 are interconnected through a parallel transfer signal line, and the PHY part 13 and PHY I/F part 14 are interconnected through a parallel transfer signal line.
The security part 24 has a security function which uses AES (Advanced Encryption Standard) defined by IEEE 802.15.4 to encrypt and decrypt data. The register, not shown, is a circuit for switching among circuit components to which data is transferred, for adjusting different data transmission/reception timings of the respective circuit components, i.e., the RAM 22, security part 24, and PHY part 13, for storing parameters required for the AES processing, and the like.
The host 30, installed outside, comprises a MAC part 15, a CPU 31 for executing a network layer 3, an application layer 5 and the like in software, and the like, and D/A converts internal digital signals (D) to analog signals (A) which are output from the host 30, D/A converts analog signals (A) from the outside to digital signals (D) which are captured into the host 30, and performs a variety of input/output (hereinafter called “I/O”) operations and the like.
Next, a radio communication method in the radio LSI 10B shown in FIG. 4 will be described.
The security part 24 is used when transmission data coming from the external MAC part 15 is encrypted and transmitted from the antenna 21, or when encrypted reception data from the antenna 21 is decrypted. If data is not encrypted or decrypted when it is transmitted or received, serial transmission data from the MAC part 15 in the host 30 is received by the PHY I/F part 14 during transmission, and parallelly transferred and stored in the RAM 22 through the bus 23. Since no MAC part is equipped inside, a parallel transfer is started from the RAM 22 to the PHY part 13 at the time the transmission data has been completely stored in the RAM 22, such that the transmission data is serially transferred from the PHY part 13 to the RF part 11 through the modem part 12, and transmitted from the antenna 21.
During reception, reception data received by the antenna 21 and RF part 11 is serially transferred, demodulated by the modem part 12, and serially transferred to the PHY part 13. The serially transferred reception data is parallelly transferred from the PHY part 13 to the bus 23, and stored in the RAM 22. The reception data read from the RAM 22 is parallelly transferred to the PHY I/F part 14 through the bus 23, and serially transferred from the PHY I/F part 14 to the host 30.
When data is encrypted and decrypted during data transmission and reception, a transmission follows a signal path which involves transmission data from the MAC part 31 in the host 30 (serial transfer)->PHY I/F part 14 (parallel transfer)=>bus 23 (parallel transfer)=>storage in the RAM 22=>bus 23 (parallel transfer)=>encryption by the security part 24 (parallel transfer)=>PHY part 13 (serial transfer)->modulation by the modem part 12 (serial transfer)->RF part 11->transmission from the antenna 21.
During reception, data received by the antenna 21 follows a signal path which involves RF part 11 (serial transfer)->demodulation by the modem part 12 (serial transfer)->PHY part 13 (parallel transfer)=>decryption by the security part 24 (parallel transfer)=>bus 23 (parallel transfer)=>PHY I/F part (serial transfer)->host 30.
On the other hand, the conventional MAC-equipped radio LSI 10A is provided therein with the MAC part 15 in the host 30, and the MAC I/F part 16, instead of the PHY I/F part 14 in FIG. 4. Transmission data from a host 30′, from which the MAC part 15 is deleted, is stored in the RAM 22 through the MAC I/F part 16 and bus 23 in the radio LSI 10A. After this determination on transfer is made by the MAC part 15 in the radio LSI 10A, transmission data is read from the RAM 22 and parallelly transferred to the PHY part 13.